The present invention relates to a time-division multiplexing apparatus in a digital transmission system and, more particularly, to a diagnostic system for a time slot switching circuit which is built in this apparatus and switches between various media on a time basis.
A conventional system for monitoring an operation of a time slot switching circuit of this type uses the following method. A specific time slot is exclusively assigned for monitoring a path to monitor operations of a data memory and an address control memory constituting the time slot switching circuit, and the operation is constantly checked by monitoring data. That is, the monitoring is performed only in an on-line state.
According to this conventional monitoring method, a constant monitoring operation is basically performed. Once the monitoring operation is started, the same monitoring operation is constantly performed. In addition, the monitoring method and monitoring items fixedly serve as only a part of a time slot switching function. For this reason, for example, the conventional monitoring method cannot effectively function to provide an easy operation checking means for performing an adjusting operation and a starting operation when the apparatus is loaded on site. The conventional monitoring method cannot effectively function to provide discrimination means for determining whether or not the time slot switching function is proper to examine a failure position when a failure has occurred in an operating state of the system. In addition, the conventional monitoring method cannot effectively function to provide checking of an operation on an off-line unit of a system having an arrangement consisting of two functional units each having the time slot switching circuit, i.e., provide a means for checking that the system is normally operated upon switching between the time slots.